This invention is related to tungsten rod and methods of forming tungsten rod. More particularly, it is related to large-diameter tungsten-lanthana rod with an elongated grain structure.
Tungsten-lanthana alloys are well-known. A description of these alloys, their methods of making, and uses can be found in U.S. Pat. Nos. 5,590,386, 5,742,891, 4,923,673, 3,159,908 and 3,086,103.
In addition to the uses referenced above, tungsten-lanthana alloys are used to manufacture rocket nozzles. Rocket nozzles require high strength along the nozzle""s longitudinal axis because of the high temperatures and internal combustive forces generated during its operation. In order to provide this high strength, the tungsten-lanthana rod from which the nozzle is machined should have a microstructure in which the tungsten grains are elongated in a direction substantially parallel to the longitudinal axis of the rod. Current methods of forging and extrusion for forming large-diameter tungsten rods ( greater than 0.625 in. dia.) achieve acceptable mechanical properties but have been ineffective at producing a longitudinal grain elongation.
It is an object of the invention to obviate the disadvantages of the prior art.
It is another object of the invention to provide a large diameter tungsten-lanthana rod having a grain structure which is elongated in a direction substantially parallel to the longitudinal axis of the rod.
It is still another object of the invention to provide a large-diameter tungsten-lanthana rod having mechanical properties desirable for rocket nozzle applications.
These and other objects and advantages of the invention have been achieved by rolling large-diameter tungsten-lanthana rod at a temperature greater than 1400xc2x0 C. and less than 1700xc2x0 C. to achieve a reduction in the cross-sectional area of at least about 40%. These rolling parameters yield a large-diameter rod having an elongated grain structure which is substantially parallel to the longitudinal axis of the rod. The as-worked rod has mechanical properties desirable for rocket nozzle applications.